AIX may come with its own PC NFS client. Check if the file rpc.pcnfsd
exists in /usr/sbin. If it exists then just run it from the command prompt
by typing /usr/sbin/rpc.pcnfsd. This will enable PCs with MS XP to map
shared filesystems from AIX server.

You should have software like Hummingbird Connectivity installed on your PC.
In Hummingbird's case, when you attempt mapping from My Computer->Tools->Map
Network Drive, you should be able to see Hummingbird NFS as an additional
option besides Microsoft Windows Network.

If you haven't already done so, export the AIX filesystem/directory from the
AIX server before doing the above steps.

If you've mounted a directory on AIX, where is it mounted from? The
usual procedure to make an AIX directory available to Windows would be
to use Samba to make it a Windows share. However if the directory is
remote to AIX it seems to me you have an extra step involved here that
isn't necessary.